This invention relates to a multiplied pulse generation device and a multiplied pulse generation method that generates a multiplied pulse obtained by multiplying a detection signal outputted per specific driven amount of a driven object. This invention also relates to an image forming apparatus and an image reading apparatus, each of which is provided with the multiplied pulse generation device mounted thereon.
A conventional ink-jet printer forms an image, for example, by ejecting ink onto a recording medium such as a sheet, an OHP sheet and a post card while reciprocating a carriage in a main scanning direction. A recording head is mounted on the carriage. In such ink-jet printer, a detection signal (pulse signal) from an encoder is used to determine ejection timing of ink from the recording head. The encoder detects a travel distance of the carriage, and outputs a pulse signal every time the carriage travels a predetermined distance.
Also, for example, an image reading scanner reads an image on a document while moving an image sensor along the document. A pulse signal from an encoder is used to determine timing to read. The encoder detects a travel distance of the image sensor, and outputs a pulse signal every time the image sensor travels a predetermined distance.
In recent years, resolution for the aforementioned image recording or image reading tends to become high. However, there is a practical limit in achieving required resolution for image recording or image reading by increasing physical resolution of the encoder, due to manufacturing and cost problems of the encoder.
For the purpose of obtaining higher resolution than physical resolution of the encoder, a known method multiplies a pulse signal from the encoder to generate a multiplied pulse. Here, the term “multiply” means to multiply the frequency of the pulse signal from the encoder by N (N: natural number). The number N is called a multiplication factor.
This known multiplied pulse generation method will be particularly explained by way of FIG. 17. In FIG. 17, the encoder outputs two types of signals, pulse-A and pulse-B signals, of which phases are shifted from each other. Multiplied pulses are generated per leading edge detection of the pulse-A signal from the encoder. This method estimates, per leading edge detection, a time interval until occurrence of a next leading encoder edge, based on the last time interval between encoder edges and the second to last time interval between encoder edges. Estimation can be made, for example, by calculating a prepared estimate equation. In FIG. 17, f(α, β) indicates an estimated cycle obtained by the estimate equation where the last time interval is α and the second to last time interval is β. For example, f(tn, tn−1) indicates an estimated cycle obtained by calculating the estimate equation based on the last time interval tn and the second to last time interval tn−1. In this multiplied pulse generation method, the estimated cycle can be obtained by calculating 2B−A or 2B−(A+H) where B is the last time interval, A is the second to last time interval, and H is a correction value.
The obtained estimated cycle is divided by a multiplication factor to calculate an interval (multiplied pulse cycle) between multiplied pulses. The multiplied pulse is sequentially outputted in accordance with the calculated multiplied pulse cycle. FIG. 17 shows an example of generation of pulses multiplied by four-times. Td is the time required for various calculations from appearance of a leading edge of the phase-A signal until output of a multiplied pulse. Td is as small as can be ignored in practice in comparison with the time interval between encoder edges.
Other than the method shown in FIG. 17, there is a method of obtaining a multiplied pulse cycle simply by equally dividing the last time interval between encoder edges by a multiplication factor.
The multiplied pulses generated by the aforementioned method are updated every time an encoder edge is detected. However, the cycles of the multiplied pulses multiplied by the predetermined multiplication factor are constant between encoder edges. That is, although the method shown in FIG. 17 estimates the estimated cycle based on the past actual time intervals between encoder edges, the generated multiplied pulse merely divides the estimated cycle according to the multiplication factor. The cycles of the generated multiplied pulses are constant.
Accordingly, there is a problem in which visible discontinuities occur in consistent with encoder periods, depending on the rate of change of driving velocity of an actual driven object, the resolution of the encoder, and the multiplication factor. That is, the cycles of the multiplied pulses are discontinuously changed at encoder edges. Such discontinuous changes appear, for example, as streaky-spot patterns in the results of image recording and image reading.